1. Field of the Invention
The present invention relates to a lubrication system, especially to a forced lubrication system for a vertical shaft engine.
2. Description of Prior Arts
A traditional forced lubrication system for a vertical shaft engine, which is proposed by the applicant of the present invention previously, is shown in FIG. 6.
In FIG. 6, a vertical shaft engine has a crank case 2, an oil pan 4 constituting the lower part of the crank case 2, a vertical crank shaft 7 supported rotatably by the crank case 2, and a vertical cam shaft 12 disposed to one side of the crank shaft 7, driven by the crank shaft 7 and supported rotatably by a pair of bosses 18 which are formed at the upper wall (not shown) and the lower wall 5 of the crank case 2. A trochoid pump 20 for lubrication is housed in the lower boss 18 for supporting the lower end of the cam shaft 12 under said cam shaft 12. Lubricating oil in the oil pan 4 is sucked by the pump and fed to the parts desired to be lubricated in the engine through an oil feeding passage 26 formed in the cam shaft 12.
In the traditional system described above, the pump 20 driven by the cam shaft 12 is rotated by the crank shaft 7 at half of the speed of the crank shaft 7. Therefore, in order to feed sufficient amounts of lubricating oil to every part desired to be lubricated, the pump 20 must have a large displacement for a round, and the boss 18 housing the pump 20 must be large. Accordingly, the capacity of said oil pan 4 is decreased corresponding to the size of the pump 20. And a large pump 20 having a large displacement is naturally expensive.